1. Field of the Invention
The present invention relates to processes and apparatus for reacting high flow rates of gaseous reactants containing particulate solids in tubular reactors, and more particularly, to reacting high flow rates of oxygen and titanium tetrachloride gas which can contain or pick up particulate solid contaminants in a tubular reactor at high temperature to produce titanium dioxide.
2. Description of the Prior Art
In reactions carried out in tubular reactors where high flow rates of gaseous reactants are injected into the reactors, problems with incomplete mixing and severe erosion of the side walls of the reactors due to the presence of particulate solid contaminants in the reactants can occur. The incomplete mixing can cause less than desirable reaction results and the erosion causes contamination of the products produced with the materials forming the reactors as well as drastically shortening the lives of the reactor apparatus. For example, in the production of titanium dioxide, the gaseous reactants are heated oxygen and heated titanium tetrachloride gas which are combined in a tubular reactor at high flow rates. A high temperature oxidation reaction takes place in the reactor whereby solid titanium dioxide particles are produced. Occasionally, both the oxygen and the titanium tetrachloride gas streams utilized in the reaction contain or pick up particulate solid contaminants which impinge on the surfaces of the reactor apparatus. Such particulate solid contaminants get into the gas streams as a result of the passage of the gas streams through process equipment and piping upstream of the reactor apparatus. The process equipment and piping can contain particulate solid scale, solid particles from fluidized beds, particulate welding slag and the like. Also, a particulate solid scouring medium such as sand is often introduced into the reactor apparatus to scour titanium dioxide deposited on the walls of the reactor therefrom. The scouring medium occasionally finds its way into various upstream parts of the reactor apparatus and some of it is picked up and carried by the gaseous reactant streams. For example, if the scouring medium is being introduced into the reactor apparatus when the flow of oxygen or titanium tetrachloride is shut down, the scouring medium can flow out of the reactor into oxygen or titanium tetrachloride introduction apparatus, e.g., plenum chambers, connected to the reactor.
In attempts to solve the problems mentioned above, large plenum chambers have heretofore been utilized upstream of the reactor injection points of gaseous reactants to trap contaminants therein, and the gaseous reactants have been injected through small gaps. The use of small gaps results in high pressure drops which bring about good mixing of gases in the reactor, but the high pressure drops in the gaseous reactants require their pressurization which is very costly.
In order to operate with lower gaseous reactant pressure drops, the gaseous reactants have heretofore been tangentially injected into small annular plenum chambers which distribute them around two or more slots through which the gaseous reactants flow radially into the reactor. The use of injection through the slots brings about low pressure drops, but particulate solid contaminants carried or picked up by the gaseous reactants can be trapped in the annular plenum chambers which causes the plenum chambers to be rapidly eroded.
Thus, there are needs for improved processes and apparatus for reacting gaseous reactants in tubular reactors which bring about low pressure drops across the reactor apparatus, more uniform distribution of the gaseous reactants and better mixing of the gaseous reactants without excessive erosion due to the presence of solid particles.
The present invention provides improved processes and apparatus for reacting solid particle containing gaseous reactants in tubular reactors which meet the needs described above and overcome the deficiencies of the prior art.
A process of the present invention for reacting a high flow rate of a gaseous reactant which can contain or pick up solid particles in a tubular reactor is comprised of the following steps. The gaseous reactant to be injected is swirled in a first annular plenum chamber followed by a second larger diameter annular plenum chamber. The swirling gaseous reactant is then introduced into the reactor by way of two or more radial slots communicating the reactor with the outlet of the second plenum chamber whereby solid particles carried with the gaseous reactant are caused to flow into the reactor with the gaseous reactant and are not trapped in the first or second plenum chambers. The radial slots bring about the uniform distribution and alignment of the flow of the gaseous reactants and solid particles through the center of the reactor and thereby prevent incomplete mixing and erosion therein. In the production of titanium dioxide, the above described process is preferably utilized for injecting high flow rates of heated oxygen into the reactor.
Another process of this invention which can also be utilized for introducing a high flow rate of a gaseous reactant into a tubular reactor which meets the above described needs is as follows. The high flow rate gaseous reactant which can contain solid particles is swirled in an annular plenum chamber which includes a boot formed therein for catching the solid particles. The resulting substantially solid particle free gaseous reactant is introduced into the reactor by way of two or more radial slots communicating the reactor with the plenum chamber. A conduit is optionally provided in the plenum chamber extending from the interior of the boot to within one of the annular slots whereby the gas pressure differential between the boot and the slot causes the solid particles caught in the boot to be swept through the conduit into the reactor. The radial slots are preferably slanted in the downstream direction to facilitate the uniform distribution and alignment of the flow of the gaseous reactant and solid particles (if any) through the center of the reactor and thereby prevent incomplete mixing and erosion therein. In the production of titanium dioxide, this process is preferably utilized for injecting high flow rates of heated titanium tetrachloride into the reactor.
Apparatus for carrying out the above described processes are also provided by the present invention.
It is, therefore, a general object of the present invention to provide improved processes and apparatus for reacting solid particle containing gaseous reactants in tubular reactors.
A further object of the present invention is the provision of improved processes and apparatus for reacting high flow rates of oxygen and titanium tetrachloride gas which may contain or pick up particulate solid contaminants in a reactor for producing titanium dioxide.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows when taken in conjunction with the accompanying drawings.